This invention relates to a method and device for magnetizing and inspecting a permanent magnet assembly of a rotating electric machine and more particularly the rotor for a magneto generator.
Many types of rotating electrical machines employ a plurality of magnetic segments secured to a cylindrical member and which cooperate with an associated plurality of coil windings. One form of device of this type is the magneto generator that is utilized with many types of internal combustion engines for generating electrical power and also for firing the ignition devices of the engine.
With this type of mechanism, a plurality of segments are mounted on a cylindrical member such as the engine flywheel and formed from materials, such as alnico-base, ferrite-base, rare earth cobalt based or neodymium-iron boron magnets, which are bonded to the rotor. These materials once bonded are then magnetized by a suitable device so as to define the desired pole arrangement. Generally after the entire segments are magnetized, then the resulting assembly is tested to make sure that it is appropriately magnetized. This is done by positioning the cylinder body in a machine where it is rotated at a relatively high speed such as about 1500 rpm and the magnetic properties are tested with a coil winding. This requires rather expensive equipment.
In addition, when utilized as a magneto generator or flywheel magneto, it is the practice to form a timing mark on the cylinder body that cooperates with an appropriate sensor for sensing the angular position of the crankshaft. This assist in setting the timing for firing of the spark plug or plugs of the associated engine. Obviously it is important that this timing mark be accurately located relative to the plurality of magnets.
Thus, it is the practice also to rotate the flywheel with a sensor device so as to determine that the timing mark is appropriately located relative to the poles of the magnets. Obviously this takes several steps and actually frequently results in the necessity to move the flywheel from one apparatus to another each of which has a drive for the flywheel. Obviously this adds costs and takes up space.
A device has been proposed where the magnetizing coil is fitted with Hall elements and the distribution of the flux density (gauss value) is measured while being rotating after magnetization. Also a drive is required for rotating the flywheel at a relatively slow speed such as about 3 rpm. While this is being done, the outer surface of the rotor can be detected by laser sensor to determine that the timing mark is appropriately positioned. However, this again requires movement of the magnetized part from one piece of equipment to another and has some further objectionable characteristics.
It is, therefore, a principal object to this invention to provide an improved apparatus, which can both magnetize the permanent magnet materials and also in the same apparatus, test the magnetic properties after they have been magnetized.
It is a further object to this invention to provide an improved testing device of the type set forth in the preceding paragraph where the position and size of the timing mark can be accurately determined in the same apparatus.
A first feature of this invention is adapted to be embodied in a magnetizing and testing apparatus and a method for magnetizing a plurality of circumferentially spaced magnetic materials mounted on a cylindrical body and testing the results of the magnetization.
In accordance with another feature of the invention, the testing apparatus also tests the magnetic properties when moving the cylindrical body out of the magnetizing field so as to minimize the number of steps of operation and avoid the necessity of rotating the device in order to sense its magnetic properties.
In accordance with a still further feature of the invention, the method and apparatus also tests the size, location and height of a timing mark formed on the cylindrical body when in the apparatus.